96 CONCHOLOGIA CESTRICA. 



Shell, thin, smooth, elliptic-ovate, compressed, rounded 

 anteriorly, produced and sub-angulated posteriorly; dor- 

 sal margin behind the ligament elevated, and compressed ; 

 epidermis more or less brown, or green, rays obsolete ; 

 nacre bluish-white, and iridescent. H. 1.25, W. 2.25, T. 

 .75, inches^ 



Station, Schuylkill River, Chester County. 



Family CORBICULID^E. 



Shell, bivalve, oval, or sub-triangular ; primary teeth 

 two, or three, in each valve; laterals two; ligament 

 external. 



Animal, mantle lobes free in front, and at the base ; 

 siphons two ; foot triangular, cylindrical, or linguiform ; 

 tentacles small, triangular, pointed ; gills broad, unequal, 

 united posteriorly. , 



DIAGRAM OF THE GENERA, AND SPECIES, OF THE FAMILY 

 CORBICULID^:. 



FAMILY. GENUS. SPECIES. 



sulcatum, 



SPH.SRIUM. 

 CORBICULID^E. 



striatmum, 



stamineum, 



fabalis, 



transversum, 



rosaceum, 



partumeium, 



securis. 



virginium. 



compressum. 



Genus SPH^RIUM, SCOPOLI, 1777. 



Shell, oval, nearly equilateral, beaks prominent ; two 

 primary teeth in each valve; laterals elongated; liga- 

 ment on the longer slope. 



Animal, with two short siphons, joined at base, oral 

 tentacles short ; foot narrow, elongated. 



OBS. The small animals included in this family 



